1. Field of the Invention
The present invention relates to a semiconductor device formed using an oxide semiconductor film and a method of manufacturing the semiconductor device.
In this specification, a semiconductor device means all types of devices which can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
In recent years, a technique by which a semiconductor device typified by a transistor is manufactured using a semiconductor thin film formed over a substrate having an insulating surface has been attracting attention. Such a semiconductor device is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). As a material of a semiconductor thin film that can be applied to such a semiconductor device typified by a transistor, a silicon-based semiconductor material is widely known.
Attention has also been drawn to a technique by which a transistor is manufactured using an amorphous oxide semiconductor material instead of a silicon-based semiconductor material and is applied to an electronic device or the like. For example, a technique for manufacturing a transistor whose active layer is formed using an amorphous oxide semiconductor material containing indium (In), gallium (Ga), and zinc (Zn) and having an electron carrier concentration lower than 1018/cm3 is disclosed (see Patent Document 1).